High-Q Bragg Resonator Cyclotron Resonance Maser Experiments On A long-pulse electron beam accelerator

Experiments on high power microwave generation from cyclotron resonance maser interactions have been performed using the Michigan Electron Long Beam Accelerator (MELBA) withe-beam diode parameters: V_D = 0.6 - 0.9 MV, pulselength = 0.5 - 1.5 μs, I_D = 1 - 50 kA. We have designed and fabricated a high-Q sinusoidal Bragg resonator designed to excite high frequency CARM oscillation of the TE₃₁ cylindrical cavity mode at 18.9 GHz. Theory predicts that the total Q of 4600 (measured) should yield a low CARM starting current of 3 - 5 amps. The measured reflectivity of the TE₃₁ mode (95 % ± 5 %) at 18.93 GHz is consistent with the prediction of uncoupled single mode theory. A high quality annular electron beam of 30 - 80 amps is produced through an apertured mask-anode. The apertured electron beam has been characterized by the use of glass plate diagnostics. The measured beam velocity ratio, v ⊥ /v ‖ ˜ 0.6, was shown to be in agreement with the simulation results from EGUN-code and MAGIC electromagnetic PIC-code and the theoretical predictions from adiabatic compression theory and Busch's theorem.